1. Field of the Inventions
The invention is directed to a method for producing metal, non-rotationally symmetric rings with a constant wall thickness along their circumference, particularly cam rings, starting from hot-rolled pipe from which individual portions are severed, mechanically machined, and subsequently hardened and tempered.
2. Description of the Related Art
In the effort to reduce specific fuel consumption in automobiles and utility vehicles, possible reductions in the weight of the vehicle have become especially important. The camshaft is viewed as one possibility for potentially economizing on weight. In a first step, the solid-cast or forged camshaft was replaced by a hollow shaft and the individual cam rings were slid into the hollow shaft and connected thereto. Shrinking, soldering or welding are selected as connection techniques. More recently, it has been attempted to use hydroforming or internal high-pressure forming (IHPF) as a connection technique. The rings must have a non-rotationally symmetric shape in order to utilize a positive engagement in addition to the frictional engagement for securing.
According to the prior art, the following known techniques can be used to produce non-rotationally symmetric rings. In a first method, a hot-rolled thick-walled pipe is used as starting material. The thick-walled pipe is inserted as a bar into a multispindle machine with a bar loader and the desired non-rotationally symmetric shape is fashioned from the thick wall by means of CNC turning and CNC milling. The finish-turned or finish-milled non-rotationally symmetric rings are finally hardened and tempered. This procedure has the disadvantages of high material input (<30% yield) and the high cost of CNC turning and milling.
Another method uses a section pipe whose cross-sectional shape comes very close to the desired final shape. Portions of this section pipe are severed and the end faces are chamfered or beveled either by means of a separate turning process or by tumbling. The high cost of material for the drawn section pipe, the low cycle time for severing the portions, and the added expenditure for beveling are disadvantageous in this method.